Trailer Park has made the promotions for blockbuster movies like ‘Wonder Woman’ and ‘Baby Driver.’

When the summer movie season arrived, among the bevy of trailers for highly anticipated films, like Wonder Woman and Spider-Man, was the promo for Baby Driver. The two and a half minute trailer itself–about a young getaway driver–has been a hit with audiences, garnering more than two million views on YouTube.

The brains behind the success of viral movie trailers like Baby Driver is Trailer Park. Founded in 1994 by Jim Hale and Tim Nett (both have since left the company), the Hollywood-based studio makes promos for movies and TV shows such as Netflix’s Stranger Things 2, Power Rangers and the international trailer for Patriots Day. But part of what makes Trailer Park’s work so entertaining is the music that’s paired with each advertisement.

The studio has tapped into the popular trend of incorporating cover songs in its promotions. For example, in 2015, Trailer Park released the Comic Con first look trailer for Suicide Squad. The short video featured a slow, eerie cover of the Bee Gees song “I Started a Joke,” setting a dark tone for the movie about villains recruited to save the world. Bobby Gumm, Trailer Park’s vice president of music, said he thought of the tune the moment he saw footage of the film.

“People have been making trailers and advertisements for a long time, and you get to the point where a lot of the big songs lyrically make sense but have been overused,” says Gumm. “You can put a different spin on preexisting things that people know and it’s a way to make your campaign feel a little more fresh.”

Trailer Park has certainly benefited from this strategy–many of the company’s trailers get millions of views on platforms like YouTube. What’s more, Trailer Park’s business has flourished: The company made more than $100 million in revenue last year and has a staff of more than 500 employees, a large increase from the five-person theatrical trailer company that launched in the mid-’90s. Now the company has expanded to include services like print, motion graphics, and animation.

Trailer Park’s creative approach to music in trailers gives the company a special edge and saves money on licensing popular songs that could have a similar effect on audiences. Gumm says if a studio wants a song by Paul McCartney, Jay Z, or another famous artist, the tune could set movie studios back half a million dollars. However, tracks by indie artists or songs without huge recognition can cost between $15,000 and $20,000 — and give a lot of promotion to lesser-known musicians.

“With the cover thing, I think 10 years ago or 15 years ago, I would have loved to use them but technology wasn’t there,” says Gumm, adding this process would have meant hiring a producer, engineer, sound mixer, and artist. “We would have been into it for so much money, and if it didn’t work out, we would be in a lot of trouble.”

Now, with advanced music editing technology, an artist and engineer can make a cover in a recording booth. Trailer Park uses an in-house composer to help create some of the idiosyncratic cover songs it has used in recent years. “They have an orchestra at their fingertips,” Gumm says.

Trailer Park isn’t the only company using cover songs to market movies. In fact, when Trailer Park is asked to make a promo, it is usually competing against one or two other companies for a contract. A movie or TV studio will reach out to several trailer production firms and ask them to make samples.